This leaflet contains recommendations regarding the use of under ballast mats. The leaflet covers the field of application for Under Ballast Mats (UBM), the exigencies that can be solved by the use of UBM, the technical and physical parameters to take into account for UBM acceptance and a guide to good practices when installing the UBM as well as the limitations for their use. The leaflet also includes a discussion of the insertion of other elastic components in the track, such as soft rail pads and Under Sleeper Pads (USP).